Flexible lead electromagnetic coil assembly

ABSTRACT

A plurality of sensing coils are formed by spiral coil electrical conductor sections deposited on a flexible substrate which is formed into a cylindrical form about a central axis. The conductor sections are spaced apart by a distance equivalent to one-quarter of the circumferencial length of the cylindrical form, to define four separate coils spaced apart by 90 degrees. Coil sections are deposited in the register on opposite sides of the substrate and interconnected through the substrate. The coil pattern may be repeated in adjacent areas of the substrate to form a multi-layered coil when a number of turns of the substrate are wound around the central axis.

This application claims benefit of Provisional Application 60/007,985filed Dec. 5, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device for generating an electric field andmore particularly to such devices of small physical dimension producinga comparatively high-strength electric field.

2. Prior Art

In certain applications, physically small electrical devices are neededto produce a relatively strong electric field. Once such application isin navigation gyroscopes, particularly in a small navigation gyroscopereferred to as a Dry Tuned-Rotor Gyroscope (DTG). On particular type ofDTG is described in the paper entitled Two-Axis Dry Tuned-RotorGyroscopes: Design and Technology; William M. Mansour and CorradoLacchini, The American Institute of Aeronautics and Astronautics, Inc.,Volume 16, No. 3, May-June 1993. The DTG is a two-degree-of-freedomsensor of angular velocity about two mutually orthogonal axes. Thisclass of instruments has been adopted for a number of controlapplications, most notably in the navigation of ships, aircrafts, andother vehicles. The basic structure of one prior art DTG is shown inFIG. 1. The unit 100 shown in FIG. 1 comprises a housing assembly havinga base 101 and a cover 102. The base 101 supports a spin shaft 104 on apair of ball bearings 106. Mounted on the base 101 is a stator 107forming part of a hysteresis motor. A hysteresis ring 108 is supportedon the spin shaft. Flexibly supported on the shaft 104 is a rotor 110. Apair of permanent magnets 112, 114, which are vertically separated bymeans of a spacer 115, are mounted on rotor 110. The rotor 110 isflexibly mounted on the spin shaft 104 and is movable with respect tothe spin shaft 104 about axes in a horizontal plane extendingperpendicular to the plane of the cross section shown in FIG. 1. Torquercoils 120, 121 are mounted on a beryllium ring 122 supported on the base101 and surrounding the magnets 112, 114. A pair of pick-offs 126 ismounted on the base 101. The pick-offs are well-known sensors coilsproducing an electrical output signal which varies with a variation inthe spacing between the pick-offs and the rotor 110. It will be apparentfrom FIG. 1 that an angular displacement of the rotor 110 about an axisperpendicular to the plane of the cross section of FIG. 1 will result inan increase in the spacing between one of the two pick-offs 126 and therotor 110 and a decrease in spacing between the other of the twopick-offs 126 and rotor 110. Electrical signals produced by thepick-offs are indicative of the magnitude of the angular displacementand are employed to produce a current in the torquer coils 120, 121. Thetorquer coils produce a magnetic field in the rotor 110 imparting atorque to the rotor 110 tending to return the rotor to a position suchthat the distances between the two pick-offs 126 and the rotor 110 areagain equal.

The permanent magnets 112, 114 are ring magnets extendingcircumferentially within the rotor 110. The unit 100 comprises fourseparate pick-offs coils and four separate torquer coils. One set ofpick-offs and one set of torquer coils are disposed along a horizontallyextending x axis and equidistant from a vertical axis and are referredto as the x pick-offs and the x torquer coils, respectively. Similarly,a set of pick-offs, referred to as y pick-offs, and a set of torquercoils, referred to as y torquer coils, are disposed along a horizontallyextending y axis, extending perpendicularly to the x axis, and spacedequidistant from the vertical axis. It will be apparent that only one ofthe sets of pick-offs and torquer coils is shown in FIG. 1. The otherpick-offs and torquer coils are disposed at 90° angles from those shownin FIG. 1. In operation, signals from the x and y pick-offs are 0 in theabsence of angular displacement of the rotor 110 relative to the spinshaft 104. When such a displacement occurs about the y axis, the gapbetween one of the x pick-offs and the rotor will increase and the gapbetween the other of the x pick-offs and the rotor will decrease. Tocancel the difference between the gaps, a torque is applied about the xaxis to force the rotor to precess about the y axes. Accordingly, asignal derived from the x pick-offs is used to apply a current to the ytorquer coils until the spacing between the rotor and the two xpick-offs is again equal.

Prior art torquer coils consist of several hundred turns of fine wirecoated with an insulated coating. The coils of wire are formed or"blocked" into a special shape and bonded to maintain that shape. Twolead wires must be attached to each coil. Each of the four coils mustthen be affixed with an adhesive to the beryllium ring or the like in aprecise location which varies from unit to unit due to the lack ofprecision inherent in the blocking operation. The eight lead wires arethen soldered to a circuit board. It will be appreciated that the rateat which the rotor is returned to the level position, once it hasexperienced an angular displacement, is directly proportional to themagnetic force generated by the torquer coils. The force or momentapplied by the torquer coil is a function of the number of turns of thetorquer coil, the curved length of the coil (i.e., the length of thecoil along the circumference of the beryllium ring), as well as thecurrent in the coil. A disadvantage of the prior art arrangement is thatthe curved length of the coil is limited by the circumference of theberyllium ring which is preferably kept as small as reasonably possiblesince the diameter of the ring affects the total size of the device.Furthermore, the straight portion of the wound coil is necessarilyrelatively short since a significant portion of the overall dimension ofthe coil is consumed by the curved portion of the wound coil.Additionally, spacing between adjacent coils is necessary for electricalconnections. Thus, even though each coil theoretically may occupy 90° ofthe circumference of the ring, the straight portion of the coil, whichdetermines curved length, may occupy only about 60°. To be useful inhigh-speed missiles and the like, the gyro must be of small size andmust correct at a very high rate in order to be able to detect attitudechanges of the vehicle at a sufficiently fast rate. To obtain a highrate of correction, a rapidly varying, high-strength magnetic field isrequired. However, the amount of current that can be supplied to thesmall size coil is limited due to excessive heat which is generated inthe wire.

SUMMARY OF THE INVENTION

These and other problems of the prior art are solved in accordance withthe present invention by means of a torquer coil constructed of a flexlead circuit material in which the conductors forming the fieldgenerating coil are etched with a photochemical process on an epoxyresin substrate and covered with a vapor-deposited insulation. Inaccordance with one aspect of the invention, a plurality of spiral coilnested conductor circuit sections are formed on a longitudinallyextending strip of the flexible material and the flexible material iswound to form a cylinder in which the centers of every other one of aset of nested conductors are separated by 180°. Thus, a sequence of foursuch nested conductors, when properly placed, form two sets of opposingcoils. In one embodiment of the invention, the number of nestedconductors arranged on the flexible material comprises an integralnumber which is a multiple of four and the flexible conductors are woundin such a manner that nested conductors which are spaced apart by threeother nested conductors form a set of adjacent layers of a coil. Eachset of adjacent layers is spaced apart by 90° from circumferentiallyadjacent sets of layers. The adjacent layers of each set areelectrically interconnected to form a plurality of coils alongperpendicularly extending axes. In this manner, multiple sets of nestedconductors, etched on a longitudinally extending substrate, are arrangedto form a single multiple layer coil at each of four positionssurrounding the circumference of the device.

In one preferred embodiment, nested wire circuits forming layers of acoil are provided on both sides of a single strip of the flexiblematerial and are interconnected through the material to form adjacentlayers of a coil.

In accordance with one aspect of the invention, the flexible materialmay comprise a thin layer of a heat conducting metal, such as copper orthe like, which acts as a heat sink conducting heat away from theconductors, thereby allowing for a greater magnitude of current to beapplied to the circuit and providing increased torque.

In accordance with another aspect of the invention, the nested circuitsare each formed with right angle corners in order to obtain an increasedcurved length of the coil. Advantageously, the right angle corners avoidthe loss in curved length of the coil due to the curvature oftraditionally wound coils of conductive wires. A further advantage ofthe present arrangement is that the coils may be placed substantiallyimmediately adjacent one another around the circumference since noadditional space is needed for connections between the coils.Advantageously, a coil arrangement in accordance with this inventionuses less space and is considerably more cost effective than wound coilsusing wire conductors.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention is described in the following paragraphswith reference to the drawing in which:

FIG. 1 is a cross-sectional representation of a prior art gyroscopeapparatus;

FIG. 2 is an enlarged diagrammatic representation of a nested conductorforming a single layer of a coil;

FIG. 3 is a diagrammatic representation of a double-sided flexiblesubstrate with nested conductors on each side of the substrate formingtwo layers of a coil;

FIGS. 4 through 8 are diagrammatic representations of a plurality ofnested circuits on a single flexible substrate which may beinterconnected and formed into a cylindrical configuration to definefour, multi-layer, spaced apart coils; and

FIG. 9 is a top view of a flexible substrate formed into a cylindricalconfiguration.

FIG. 10 is a cross-sectional view of a metallic substrate covered withan insulating layer and conductors deposited on both sides of thesubstrate.

DETAILED DESCRIPTION

FIG. 2 is a top view of a single nested circuit comprising a strip ofconductive material 201 in the form of a spiral coil nested conductorcircuit section 260, deposited on a substrate 203 which may be awell-known flex lead circuit material with a copper conductor or thelike etched onto the substrate. The conductor has one end 205 which, bymeans of an opening in the substrate known as a "via", may be connectedto an adjacent nested circuit. The adjacent circuit may be eitherdeposited on the opposite side of the substrate or deposited on anothersection of the substrate which, when the substrate is formed into acylindrical form, is in alignment with the section to form a next layerof a coil.

In a preferred embodiment of the invention, a nested circuit isdeposited on both sides of the flexible substrate. FIG. 3 is a top viewof a nested circuit configuration 230 on one side of the substrate,referred to herein as the top side of the substrate. A second nestedcircuit configuration 235 is deposited on the other side of thesubstrate. Via 231 of circuit 230 and via 236 of circuit 235 arerespectively connected to a current source and a current sink. Vias 232and 237 are interconnected through the substrate to form a continuouscircuit. The conductors are preferably arranged on opposite sides of thesubstrate in such a fashion that conductor sections on opposite sides ofthe substrate are in register with each other. This is shown further inFIG. 4 described below. The complementary nested conductors, i.e,arranged in register on opposite sides of the substrate, do notnecessarily have the same electrical length but the overall electricallength is the same for each complementary set.

FIGS. 4 through 7 form a schematic representation of an arrangement of16 complementary sets of nested conductors. In each case, the drawingshows a top view of the nested conductor on one side of the substrate aswell as the top view of the nested conductor on the reverse side of thesubstrate, as viewed from the one side of the substrate. The nestedconductor sets are numbered 1A, 1B through 16A, 16B. A specific patternis indicated for each of the nested conductors of sets 1A, 1B through8A, 8B. Each pair of nested conductors forms two layers of a coil and,since there are four torquer coils in the gyroscope of FIG. 1, each setof 8 complementary nested conductors represents four layers for each ofthe four coils. As stated in connection with FIG. 3, the conductors ofthe complementary nested circuits A and B of each pair are arranged inregister with each other on opposite sides of the substrate. Thesubstrate with the sets of nested conductors is formed into amulti-layer cylindrical unit in such a manner that for each completeturn of the substrate one complementary pair of the nested circuits isaligned with one torquer coil position. Thus, in one complete turn ofthe substrate, two layers are added to each of the four coils. For thesake of this description, the side of the substrate facing outwardlyfrom the center of the gyroscope arrangement is referred to as the topside and the side of the substrate facing inwardly is referred as thebottom side. In accordance with that convention, nested circuits 1A, 2A,etc. are formed on the top side of the substrate and nested circuits 1B,2B, etc. are formed on the bottom side of the substrate. It will beapparent that in such a configuration, the nested circuit 5B will beplaced in alignment with nested circuit 1A. Nested circuit 5B ispreferably arranged such that when placed adjacent to the nested circuit1A the conductor sections of nested circuit 5B fall between conductorsections of the nested circuit 1A. Advantageously, such a nestingarrangement provides volumetric efficiency by reducing the overallthickness of multiple turns of the substrate in forming the multi-layercylindrical unit. In a similar fashion, the nested circuit 6B is nestedin circuit 2A, circuit 7B is nested in circuit 3A, and circuit 8B isnested in circuit 4A. Similarly, after a subsequent complete turn of thesubstrate, circuits 9B through 12B are nested in circuits 5A through 8,respectively. The specific patterns of nested circuits 1A through 8A arerepeated in nested circuits 9A through 16A. Similarly, the patterns ofnested circuits 1B through 8B are repeated in 9B through 16B. Asindicated earlier, the nested circuit patterns 1A, 1B through 8A, 8Brepresent four layers of each of four separate coils. Similarly, nestedcircuits 9A, 9B through 16A, 16B represent four additional layers foreach coil. The patterns of circuits 1A, 1B through 8A, 8B may berepeated as many times as required to obtain the desired number oflayers in each coil.

FIG. 8 is a cross-sectional view of a portion of a plurality of layersof the substrate 200 wound a number of times around a cylindrical form.FIG. 8 shows the deposit of conductors, e.g., conductors 240 and 241, onopposite sides of the substrate 200 and in register with each other.FIG. 8 further shows the nesting arrangement in which a conductor on onesubstrate, e.g., conductor 241, is disposed in a spacing betweenadjacent conductors, e.g., 243, 244, allowing nesting of conductors ofone nested circuit in a spacing between conductors of a nested circuiton an adjacent section of the substrate. FIG. 8 further shows aninsulating layer 250 on each side of each section of the substrate whichcovers the conductor sections, such as 241, 243, and 244, to assureproper insulation between adjacent conductors. Space between adjacentlayers of the substrate not occupied by conductors, such as the spaceindicated at 251, is filled with a resin.

FIG. 9 is a schematic representation of a nested circuit 260 disposed onan outer surface of one layer of the substrate, with the substrate woundin the cylindrical form, and another circuit 270 disposed on the innersurface of a next layer of the substrate. The nested circuit 260represents one of the patterns of nested circuits, e.g., 1A of thecircuits represented in FIGS. 4 through 7, and conductor 270 representsanother circuit with a specific pattern, e.g., the pattern of nestedcircuit 5B, of one of the circuits of the arrangement of FIGS. 4 through7.

FIG. 10 is a top view of a cylinder formed by winding the substrate 200around a cylindrical form 280 used in the construction of a multi-layer,multi-coil configuration for use in a gyroscope or the like. Only threewraps of the substrate are shown in FIG. 10. After 15 or 20, such wrapsmay be wound around the core to form the multi-coil configuration inaccordance with the invention. A wall of radially increasing thickness282 is disposed external to the core. The wall has a thickness at leastequal to the thickness of the substrate and conductors disposed on bothsides of the substrate. This provides a starting point for winding thesubstrate around the core in an essentially a spiral fashion. A first90° section 284 of the substrate incorporates two nested circuits, e.g.,circuits 1A and 1B shown in FIG. 4, on opposing sides of the substrate.A second 90° section 285 of the substrate 200 includes a further pair ofnested circuits, e.g., 2A, 2B of FIG. 4. Similarly, third and fourthsections 286, 287 may correspond to the section of the substrateincorporating nested circuits 3A, 3B and 4A, 4B, respectively of FIG. 4.For the sake of simplicity, the drawing of FIG. 10 does not show thenesting between circuits of adjacent layers but serves to illustrate theforming of the cylinder. In the configuration of FIG. 10, the opposingsections 284 and 286 may be considered to correspond to opposing torquercoils along the x axes in the configuration of FIG. 1. Similarly,sections 285, 287 of FIG. 10 may be considered as corresponding toopposing torquer coils along the y axes, extending perpendicular to thex axes. It will be apparent from the description in connection with FIG.8 and FIG. 10 that each additional turn of the substrate 200 with nestedcircuits disposed on both sides thereof will add circuit layers to eachof the x and y torquer coils. After the coils have been completelyformed by winding of the substrate around the core 280, the entire unitis encapsulated in a resin to maintain the substrate in the desired formand position. The unit may then be removed from the core 280 andinstalled in a gyroscope in a configuration similar to that of torquercoils 120, 121, shown in FIG. 1.

What is claimed is:
 1. An electromagnetic coil assembly comprising:alongitudinally extending flexible substrate formed into a cylindricalform having a plurality of layers and an exterior circumferential lengthand a central axis; a plurality of spiral coil electrical conductorsections disposed on the substrate and spaced apart by a distanceequivalent to one quarter of the exterior circumferential length to formtwo pairs of opposing coils, each spiral coil conductor section having aplurality of spaced apart turns and a center and a central electricalconnection terminal adjacent the center and an exterior terminal end andan exterior electrical connection terminal adjacent the exteriorterminal end; wherein a first spiral coil electrical conductor sectionon a one side of a first layer is disposed in register with a secondspiral coil electrical conductor section on one side of second layerdisposed adjacent the one side of the first layer and wherein spacedapart turns of the second spiral coil electrical conductor section arenested between spaced apart turns of the first spiral coil electricalconductor section.
 2. The coil assembly in accordance with claim 1wherein the substrate comprises opposite sides and the assembly furthercomprises a first set of the spiral coil electrical conductor sectionson one of the opposites sides of the substrate and a second set of thespiral coil electrical conductor sections on another of the oppositesides of the substrate and wherein each of the electrical conductorsections of the second set is disposed in register with an electricalconductor section of the first set and each pair of electrical conductorsections disposed in register forms two adjacent layers of a coil. 3.The coil assembly in accordance with claim 2 wherein the centralelectrical connection terminals of a pair of the electrical conductorsections disposed in register is electrically interconnected through thesubstrate.
 4. The coil assembly in accordance with claim 1 wherein thelongitudinally extending substrate is formed into a cylindrical formcomprising a plurality of layers of the substrate and wherein each layercomprises four of the spiral coil electrical conductor sections.
 5. Thecoil assembly in accordance with claim 4 wherein the substrate comprisesopposite sides and wherein a layer of the substrate further comprises afirst set of the spiral coil electrical conductor sections on one of theopposites sides of the substrate and a second set of the spiral coilelectrical conductor sections on another of the opposite sides of thesubstrate and wherein each of the spiral coil electrical conductorsections of the second set is disposed in register with a spiral coilelectrical conductor section of the first set and each pair ofelectrical conductors disposed in register form two adjacent layers of acoil.
 6. The coil assembly in accordance with claim 5 wherein thecentral electrical connection terminals of a pair of electrical spiralcoil conductor sections disposed in register on opposite sides of thesubstrate are electrically interconnected through the substrate.
 7. Thecoil assembly in accordance with claim 6 wherein exterior electricalconnection terminal of a selected spiral coil electrical conductorsection on one side of one layer of the substrate is electricallyconnected to the exterior electrical connection terminal of a spiralcoil electrical conductor section disposed on an adjacent layer of thesubstrate disposed in register with the selected spiral coil electricalconductor section.
 8. The coil assembly in accordance with claim 5wherein a first spiral coil conductor section on one side of a firstlayer of the substrate is disposed in register with a second spiralconductor section on other side of a second adjacent layer of thesubstrate and wherein adjacent turns of the first section are spacedapart and adjacent turns of the second conductor section are spacedapart and formed to be fitted between adjacent turns of the first spiralcoil conductor section.
 9. The coil assembly in accordance with claim 1wherein the spiral coil electrical conductor sections each comprise aplurality of turns and each turn comprises logitudenally extending andsubstantially straight conductor sections joined at substantially rightangles.